Conventional methods for producing metal oxide sols, such as a zirconia sol, for example, include a method in which an aqueous solution of a zirconium salt is hydrolyzed with heating, a method in which hydrogen peroxide is added to an aqueous solution of a zirconium salt and the solution is heated, a method in which zirconium hydroxide is heated in the basic region, and the like.
A method has been described in Japanese Patent Application Publication No. JP-A-3-174325 (Claims) in which a reaction product of zirconium ammonium carbonate and a chelating agent (for example, an oxyphenol, an amino alcohol, an oxylate, a polycarboxylic acid, an oxyaldehyde, an amino acid, or a β-diketone) is hydrolyzed.
A method for producing a basic zirconia sol has been described in Japanese Patent Application Publication No. JP-A-64-83519 (Claims) in which an aqueous suspension containing crystallized zirconia is produced by holding an aqueous suspension containing zirconium hydroxide in a heated state at a temperature of at least 80° C. until the extent of crystallization of the zirconia that is formed reaches 80% or higher. A basic compound containing nitrogen (primary amine, secondary amine, or quaternary ammonium hydroxide), or a hydroxide of an alkaline metal or an alkaline earth metal, is then added to the aqueous suspension containing crystallized zirconia to manufacture the basic zirconia sol.
A method for producing a zirconia sol has been described in Japanese Patent Application Publication No. JP-A-60-176920 (Claims) in which a base is added to an aqueous solution of a zirconium salt to cause precipitation, and a suspension is produced by adding a hydroxide of an alkaline earth metal, or an aqueous solution thereof. The suspension is then heat aged at a temperature of 90° C. to 200° C. to form the zirconia sol.